787 Batteries and Chargers - Part 1

[RR_NDB]

Duty cycle of batteries

Hi,

Questions:

Typically in the 787 commercial operation the APU and MAIN batteries how long probably operated supplying current? I.e. :
1) APU battery started occurred frequently? Certainly not. Towing? Yes, but at low amps and few minutes. Low discharge.
2) MAIN battery (probably only on ground (tarmac, towing and hangar) operated (estimated) how many hours ? (each plane)

I suppose in both uses (APU and MAIN) the use (time) was low. (compared to their capacity).

So we could expect they were most of time being charged (most time being "trickle charged" or charged with high nominal charge current during few minutes)

I think we may say say these batteries exhibited a low MTBF despite a light use. (MAIN battery is "out of the bus" if BUS voltage is "normal" (gennies ok).

Exceptions: Possible spikes as suggested by fizz57 @ (#337) (probably much larger than 1C (65 Amps)

This "electrical environment" aspect is perhaps the last one we may imagine (characteristic of the 787) if chargers, BMS algorithms or defective components are to be discarded as causing the low MTBF.

I aasume the designers put a way to not allow discharge of ANY cell below a "safe" voltage. Remember you CAN´T depend on these batteries too long at ground. GPU, APU or engine gennies are essential for (prolonged) prolonged use. And a "automatic" disconnection shoul be adopted. (due a limitation of cells).

This may explain part of the low battery MTBF of the fleet.